Wednesday, July 05, 2017

Pictured
above is a zoomed-in image of the Little Cub galaxy, a star-forming
dwarf galaxy that is being stripped of gas by its gigantic neighboring
galaxy. Credit: SDSS COLLABORATION

A
false color image shows the grand design spiral galaxy NGC 3359, which
is about 50 million light years from Earth. NGC 3359 appears to be
devouring a much smaller gas rich dwarf galaxy, nicknamed the Little
Cub, which contains 10,000 times fewer stars than its larger companion.
The contours show where the gas is being stripped from the Little Cub,
whose stars are located in the central blue circle. Credit: SDSS COLLABORATION

Maunakea, Hawaii – Astronomers have spotted a primitive galaxy being
devoured by a gigantic neighboring galaxy – a discovery that could provide
clues about the early universe.

The Little Cub galaxy – so called
because it sits in the Ursa Major or Great Bear constellation – is being
stripped of the gas needed to continue forming stars by its larger companion.

This rare opportunity to observe
a dwarf galaxy as its gas is removed by the effects of a nearby giant galaxy
will allow scientists to learn more about how this process happens.

Since
the Little Cub has remained almost
pristine since its formation, scientists also hope its elements will reveal
more about the chemical signature of the universe just minutes after the Big
Bang.

The research, carried out by the
University of California, Santa Cruz and Durham University, United Kingdom, is
being presented on Tuesday, July 4, at the Royal Astronomical Society’s
National Astronomy Meeting.

The Little Cub was initially
identified as a potentially pristine dwarf galaxy in data from the Sloan
Digital Sky Survey (SDSS). Follow-up observations were conducted at the
10-meter Keck I telescope at the W. M. Keck Observatory on Maunakea, Hawaii,
and the 3-meter Shane Telescope at Lick Observatory.

Researchers were able to confirm characteristics
of the Little Cub galaxy using Keck Observatory’s Low Resolution Imaging
Spectrograph, a faint-light instrument capable of taking spectra and images of
the most distant known objects in the universe.

"The Little Cub's discovery
is a terrific example of using the smaller 3-meter-class Lick Observatory to
scan through hundreds of candidates before focusing on the best sources with the
Keck telescope," said co-author J. Xavier Prochaska, Professor of
Astronomy and Astrophysics at UC Santa Cruz.

The Little Cub’s larger
neighbor, called NGC 3359, is a grand design spiral galaxy, which is a large
galaxy that has over 100 billion stars with well-defined spiral arms – similar
to our own Milky Way galaxy. The Little Cub and NGC 3359 are about 200 to 300
thousand light years apart, and approximately 50 million light years from
Earth.

Gas from the Little Cub is being
stripped away by its interaction with NGC 3359, which has up to 10,000 times as
many stars as the Little Cub and is similar to our Milky Way.

By observing this cosmic feast,
scientists hope to understand more about how and when gas is lost from smaller
galaxies.

“We may be witnessing the
quenching of a near-pristine galaxy as it makes its first passage about a Milky
Way-like galaxy," said lead author Tiffany Hsyu, a graduate student in the
Department of Astronomy & Astrophysics at UC Santa Cruz. “It is rare for
such a tiny galaxy to still contain gas and be forming stars when it is in
close proximity to a much larger galaxy, so this is a great opportunity to see
just how this process works. Essentially the larger galaxy is removing the fuel
that the Little Cub needs to form stars, which will eventually shut down star
formation and lead to the smaller galaxy’s demise.”

The
researchers also hope to gain insight into the make-up of the very early universe,
by studying the hydrogen and helium atoms that are being illuminated by the
small number of very bright stars within the Little Cub – which also has the
less romantic name SDSS J1044+6306. Since this galaxy is so primitive, it may
still preserve the hydrogen and helium atoms that were created minutes after
the Big Bang.

“By studying the chemistry of the
Little Cub, we know that it is one of the most primitive objects currently
known in our cosmic neighborhood,” said research co-author Dr. Ryan Cooke,
Royal Society University Research Fellow, in Durham University’s Centre for
Extragalactic Astronomy.

“Such galaxies, which have
remained dormant for most of their lives, are believed to contain the chemical
elements forged a few minutes after the Big Bang.By
measuring the relative number of hydrogen and helium atoms in the Little Cub we
might be able to learn more about what made up the Universe in the moments after
it began 13.7 billion years ago,” Cooke added.

The researchers hope further
observations will find more pristine galaxies where the chemical signature of
the early universe might be found.

A paper describing the discovery
of Little Cub has been submitted for publication in the Astrophysical Journal Letters.

The research was funded by the W.
M. Keck Foundation, Google, The Royal Society, NASA, the Science and Technology
Facilities Council and the National Science Foundation (USA).

The Royal Astronomical
Society’s National Astronomy Meeting is taking place at the University of Hull,
UK, until Thursday, July 6, 2017.

About LRIS

The Low Resolution
Imaging Spectrometer (LRIS) is a versatile visible-wavelength imaging and
spectroscopy instrument commissioned in 1993 and operating at the Cassegrain
focus of Keck I. Since it has been commissioned it has seen two major upgrades
to further enhance its capabilities: addition of a second, blue arm optimized
for shorter wavelengths of light; and the installation of detectors that are
much more sensitive at the longest (red) wavelengths. Each arm is optimized for
the wavelengths it covers. This large range of wavelength coverage,
combined with the instrument's high sensitivity, allows the study of everything
from comets (which have interesting features in the ultraviolet part of the
spectrum), to the blue light from star formation, to the red light of very
distant objects. LRIS also records the spectra of up to 50 objects
simultaneously, especially useful for studies of clusters of galaxies in the
most distant reaches, and earliest times, of the universe. LRIS was used
in observing distant supernovae by astronomers who received the Nobel Prize in
Physics in 2011 for research determining that the universe was speeding up in
its expansion. Support for this project
was generously provided by the Change
Happens Foundation, Mt. Cuba Astronomical Foundation, William J. and Dorothy K.
O’Neill Foundation, and Sanford and Jeanne Robertson.

About W. M. Keck Observatory

The W. M. Keck
Observatory operates the most scientifically productive telescopes on Earth.
The two, 10-meter optical/infrared telescopes on the summit of Maunakea on the
Island of Hawaii feature a suite of advanced instruments including imagers,
multi-object spectrographs, high-resolution spectrographs, integral-field
spectrometers, and world-leading laser guide star adaptive optics systems. The
Observatory is a private 501(c) 3 non-profit organization and a scientific
partnership of the California Institute of Technology, the University of
California, and NASA.